1. Field of the Invention
The present invention relates to an inverter-driven rotating machine system, a rotating machine and inverter used in it and an electric vehicle using it.
2. Description of the Related Art
In recent years, for the purpose of energy saving, inverter supplies are widely used for adjustable speed drive of rotating machines. However, driving a rotating machine with an inverter supply may pose a problem of degrading electrical insulation in the rotating machine which may be attributable to steep fronted surge voltages from the inverter. Conventionally, for these inverter surge voltages, countermeasures such as enhancing the internal insulation are implemented on the rotating machine side.
Meanwhile in recent years, inverter-driven rotating machine systems for hybrid electric vehicles are directed to a system where the internal DC voltage of the inverter is boosted to make the inverter-driven rotating machine system smaller and more efficient so that the inverter-driven rotating machine system is improved in power density without enlargement in size. Further, for inverter-driven rotating machine systems for fuel-cell vehicles and other electric vehicles which use the inverter-driven rotating mechanism as not merely the engine assist mechanism but the main driving mechanism, it is possible that the voltage may be further boosted in order to make them smaller, lighter and more efficient.
However, boosting the DC voltage of the inverter results in a higher surge voltage generated in the inverter each time a LGBT or other high speed power semiconductor device is turned ON/OFF. Further, arriving at the end of the rotating machine, this surge voltage from the inverter side may be multiplied.
To reinforce the rotating machine in terms of insulation to cope with these high voltage surges, the rotating machine becomes larger.
Accordingly, we think it will become necessary to employ a method of reducing the surge voltage outside the rotating machine in combination with the reinforcement of insulation inside the rotating machine.
There are known methods for reducing the surge outside the rotating machine. For example, in order to suppress the increase of surge voltage from the cable to the rotating machine, a sinusoidal output filter or a reactor is connected to the output terminal of the inverter to mitigate the steep rise of the surge voltage or a filter unit is set at the end of the rotating machine to absorb steep voltage components of the surge voltage (for example, GAMBICA/REMA: VARIABLE SPEED DRIVES AND MOTORS Motor Insulation Voltage Stresses Under PWM Inverter Operation: A GAMBICA/REMA Technical Report No. 1 (Non-Patent Document 1)).
In addition, cables designed to absorb surge voltage were recently proposed (for example, JP-A-2005-183654).